Secretome of human endothelial cells under shear stress.

Endothelial cells are exposed to different types of shear stress which triggers the secretion of subsets of proteins. In this study, we analyzed the secretome of endothelial cells under static, laminar, and oscillatory flow. To differentiate between endogenously expressed and added proteins, isolated human umbilical vein endothelial cells were labeled with l-Lysine-(13)C(6),(15)N(2) and l-Arginine-(13)C(6),(15)N(4). Shear stress was applied for 24 h using a cone-and-plate viscometer. Proteins from the supernatants were isolated, trypsinized, and finally analyzed using LC-MS/MS (LTQ). Under static control condition 395 proteins could be identified, of which 78 proteins were assigned to the secretome according to Swiss-Prot database. Under laminar shear stress conditions, 327 proteins (83 secreted) and under oscillatory shear stress 507 proteins (79 secreted) were measured. We were able to identify 6 proteins specific for control conditions, 8 proteins specific for laminar shear stress, and 5 proteins specific for oscillatory shear stress. In addition, we identified flow-specific secretion patterns like the increased secretion of cell adhesion proteins and of proteins involved in protein binding. In conclusion, the identification of shear stress specific secreted proteins (101 under different flow conditions) emphasizes the role of endothelial cells in modulating the plasma composition according to the physiological requirements.